At present, photographic materials using silver halide photographic emulsions are used for various purposes in the market, and the market for such materials has been increasing in recent years.
In these circumstances, shortening the development processing time of photographic materials used where there is strong demand to finish a large amount of prints in a short delivery time, particularly as in the case of photographic materials for color prints leads directly to improved production efficiency of the prints so that many studies on increasing developing speed have been made.
It is well known that developing speed is greatly improved when the content of silver chloride in the silver halide emulsion used in the photographic materials is increased. However, it has been known that the use of an emulsion high in silver chloride content is accompanied by such defects as high fogging, that high sensitivity is difficult to obtain, that the so-called reciprocity law failure, which results in a change of sensitivity due to a change in exposure illuminance, is large, and that the sensitivity also changes greatly due to a change in temperature at the time of exposure.
Various techniques have been disclosed to overcome the above defects involved in silver halide emulsions high in silver chloride content (hereinafter referred to as high-silver chloride emulsion).
For example, JP-A ("JP-A" means unexamined published Japanese patent application) Nos. 95736/1983, 108533/1983, 222844/1985, and 222845/1985 disclose that in order to render high-silver-chloride emulsions highly sensitive, it is effective to make the silver halide grains have various structures, for example a layer high in silver bromide content. However, as a result of study by the inventors it has been found that, according to these techniques, although the sensitivity does indeed increase, when the emulsion grains undergo pressure, desensitization is liable to take place, which is a major defect in practice. Further, with these techniques it has also been found that it is difficult to reduce sufficiently the reciprocity law failure involved with a high-silver chloride emulsion.
For example, JP-A No. 139323/1976 or 171947/1984 or British Patent Specification 2109576A describes that when a compound of a metal of Group VIII is added, high sensitivity can be obtained and the reciprocity law failure can be reduced. JP-B ("JP-B" means examined Japanese patent publication) No. 33781/1974, JP-A No. 23618/1975, 18310/1977, 15952/1983, 214028/1984, or 67845/1986, German Patent No. 2,226,877 or 2,708,466, or U.S. Pat. No. 3,703,584 describes that high contrast and a reduction in reciprocity law failure can be attained by the inclusion of a rhodium compound or an iridium compound. However, when a rhodium compound is used, although an emulsion high in contrast can be obtained, extreme desensitization occurs, which is not preferable in practice. And, when an iridium compound is used, so-called latent-image sensitization, wherein the development density often increases with the passage of time from the exposure of the photographic material to processing, is observed conspicuously, which is also not preferable in practice.
Further, U.S. Pat. No. 4,269,927 describes that when cadmium, copper, zinc, or a mixture of these is contained within surface-sensitive high-silver chloride emulsion grains having a silver chloride content of 80 mol % or over, high sensitivity can be obtained. However, although this technique has a small effect in increasing sensitivity and in reducing reciprocity law failure, the lessening of sensitivity fluctuation due to a change in temperature at the time of exposure was not sufficient.
JP-B No. 35373/1973 describes that a high-contrast black and white photographic paper can be obtained inexpensively by the inclusion of a water-soluble iron compound into a silver chloride emulsion produced by a single-jet process. However, with this technique it is difficult to obtain an appropriate effect because if the amount of the iron compound to be added is increased to attain high sensitivity, desensitization is liable to occur when the emulsion undergoes pressure.
Further, JP-A No. 183647/1989 describes an improved technique wherein when silver bromide localized phases are allowed to be present within high-silver chloride emulsion grains containing iron ions or on the surface thereof, high sensitivity can be obtained and the fluctuation of sensitivity due to a change in temperature at the time of exposure can be made small. However, this technique still has an unsolved problem in that the introduction of silver bromide localized phases means that desensitization is apt to occur when the emulsion grains undergo pressure.